The present invention relates to the architecture of a packet switching system having self-routing switches.
As described in "Digital Switching System" edited by The Institute of Electronics and Communication Engineers of Japan, Mar. 15, 1986, pp. 128-130, a conventional multi-processor type switching system is so constructed as to use the function distribution and the load distribution in combination wherein the switching processing function is divided into a plurality of blocks which are allotted to individual processors. Additional processors of the same function as that of the individual processors are further provided in accordance with the magnitude of the load.
The function distribution faces the following problems:
(1) A fault of, for example, software in one of the processors influences the whole system very greatly. PA0 (2) The interface between processors depends on the method of dividing the function and with loose interface, the process overhead generally tends to increase. PA0 (3) Even the minimum scale of construction of the system has a plurality of processors. In digital switching systems, even when the load distribution is adopted in order to let one processor (unit) have completely independent function, such control as path setting with respect to each call is required in the tandem unit adapted to perform connection between units, as the capacity of the system increases.
For the purpose of improving the switching throughput, the self-routing switching system is promising being that it realizes packet switching processing using a packet of fixed length, as represented by the asynchronous transfer mode (ATM), in terms of hardware. An example of load distribution architecture of an ATM switching system using self-routing switches is disclosed in "A Study on the Architecture of the ATM Switching Network", Technical Report SSE-38 of The Institute of Electronic Information and Communication Engineers of Japan, Jul. 19, 1989. However in this example, a module for coupling distributed modules includes a control processing for performing a packet header processing, raising a similar problem to that in function distribution as described above.
In the aforementioned conventional systems, a switching unit (tandem unit) adapted to couple switching units for load distribution (local units) must perform control for path setting in respect of each call and the control signal must be terminated so as to carry out part of the switching processing. This leads to problems that reliability of the tandem unit causes a bottleneck in the system and even the minimum construction needs the tandem unit together with the local units.